1. Field of the Invention
The present invention is directed to a method and a device for increasing elevator safety by triggering appropriate emergency stops or other safety devices in the event the elevator cage deviates from the travel curve by more than predetermined safety margins.
2. Discussion of Background Information
Modern elevators have an elevator control which computes travel parameters for a travel of an elevator cage for an individual elevator cage and/or for groups of cages according to optimized algorithms and applicable safety regulations. The elevator control passes these travel parameters to a control for a cage drive, as described in, for example, patent specification EP 0 100 095, the disclosure of which is incorporated by reference in its entirety. Usually, and as evident from patent specifications DE 3 818 083 and U.S. Pat. No. 4,887,695, the disclosures of which are incorporated by reference in their entireties, additional means for monitoring the travel curve of the elevator cage are used for control of the cage drive. The travel curve represents a certain position of the cage at a certain time, and is corrected by control of the cage drive. In that case, only such deviations from the travel curve are permissible as lie within a certain, mostly prescribed, safety margin. When the safety margin is exceeded, safety is endangered.
Although these means for monitoring the travel curve for the control of the cage drive can ascertain deviations of the elevator cage from the computed travel curve, they are not, due to their direct connection with the cage control, suitable and/or permitted as a safety device for monitoring current failure, for example, for triggering a safety switch. Consequently, additional means, which are independent of the control of the cage drive, are necessary to monitor failure of the cage drive, cable fracture, current failure, excessive speed of the elevator cage, or any other impermissible disturbance, and to trigger an emergency stop or another safety device of the elevator cage.
Speed limiters are known in particular which, as described in, for example, patent specification EP 0 498 597, the disclosure of which is incorporated by reference herein in its entirety, at excessive speeds of the elevator cage in one of the directions of travel, mechanically trigger a braking system, denoted as an arresting device. Tachometers, which have a voltage dependent on speed for the triggering of a braking system (see, e.g., U.S. Pat. No. 5,366,045 or DE 2 128 662) are known. It is also known to utilize acceleration sensors for the recognition of disturbances (see, e.g., DE 3 934 492). The disclosures of each of the above-noted documents are incorporated by reference herein in their entireties. A significant disadvantage of these safety systems is that the emergency stop, which is triggered in the case of a corresponding disturbance, always takes place through an arresting device of the elevator cage. This often leads to a substantial jerking or jarring of the elevator cage, to difficultly releasing wedging of the brakes with the guide elements of the elevator cage and/or to damage of these parts. Moreover, in certain cases these safety systems have a relatively large delay. Thus, for example, a cable fracture or a current failure leads to a triggering of the arresting device only when excessive acceleration or speed triggers the corresponding system. None of the known safety systems is capable of recognizing deviations from the position, the speed and the acceleration of the elevator cage. Optical, electronic, electromagnetic or other sensors, for example, a distance-measuring device operating with laser beams, are known and can ascertain position, speed, and acceleration. However, these devices cannot ensure the required safety. Further, these systems are very susceptible to faults, for example, due to electromagnetic fields, dust, or vibrations, and therefore, require a very high effort for maintenance, calibration and upkeep. These devices have a direct as possible mechanical connection between the recognition of an impermissible deviation and the triggering of a safety device, which is usually required.